The vertebrate lung develops via a process known as branching morphogenesis, wherein subgroups of epithelial cells are instructed reiteratively to form clefts or buds and thereby generate a space-filling tree with a sufficient surface area for gas exchange to support breathing after birth. An aberrant mechanical environment within the thoracic cavity can disrupt branching and cause fetal pulmonary hypoplasia, a major cause of respiratory insufficiency of the newborn. It is unclear how mechanical stresses control or disrupt the branching program. Here, we describe experiments combining tissue engineering approaches with investigations of intact embryonic lungs to define how mechanical stresses are transduced into gene expression changes that drive branching morphogenesis. Engineered lung tissues and computational models will be used to predict the role of mechanical stresses in branch site initiation. In Specific Aim 1, we will determine whether and how mechanical stresses regulate branching morphogenesis of engineered embryonic mouse lung tissues and intact chick and mouse embryonic lungs. In Specific Aim 2, we will define the mechanically induced gene expression changes that drive lung branching. To our knowledge, this work will represent the first comprehensive analysis of mechanically responsive genes in branching morphogenesis in culture or in vivo. We expect that the gene expression patterns revealed will uncover new avenues to explore for medical treatment of mechanically-induced diseases such as fetal pulmonary hypoplasia. PUBLIC HEALTH RELEVANCE: Organ development requires exquisite control processes to ensure proper patterning and generation of functional forms. Increasing evidence suggests that mechanical stresses are involved in the development of the branching patterns of the lung and other tree-like organs, and that aberrant mechanical stresses can cause human fetal pulmonary diseases. We present here an integrated approach to define precisely how mechanical stresses are converted into gene expression changes that drive branching morphogenesis of embryonic lung tissues, which will enable future studies to treat human fetal pulmonary disease.